Detector for a physical quantity having a self-testing function

ABSTRACT

A fixed substrate (10) having rigidity and a flexible substrate (20) having flexibility are arranged in such a manner that they are opposite to each other. Both the substrates are fixed at their peripheral portions by a detector casing (40). A working body (30) is connected onto the lower surface of the flexible substrate. Test electrodes (11t, 13t, 15t) are formed on the lower surface of the fixed substrate, and fixed electrodes (11, 13, 15) are further formed through an insulating layer (16). Displacement electrodes (21, 23, 25) are formed on the upper surface of the flexible substrate. When an acceleration is exerted on the working body, the flexible substrate is bent, so the distance between the fixed electrode and the displacement electrode is varied. By detecting the change of distance as a change of the electrostatic capacitance between both the electrodes, it is possible to detect an acceleration exerted. In order to carry out the operation test of this detector, a voltage is applied across the test electrode and the displacement electrode, thus allowing coulomb force to be exerted between both the electrodes. Thus, the flexible substrate is bent by coulomb force, resulting in the same state as the state where an acceleration is exerted. By examining a change of the electrostatic capacitance between the fixed electrode and the displacement electrode, the operation test can be conducted.

TECHNICAL FIELD

This invention relates to a method of testing the operation of anapparatus for detecting a physical quantity such as force, accelerationor magnetism, etc. utilizing changes in distance between electrodes, andfurther relates to a detector for a physical quantity such as force,acceleration, or magnetism, etc., having a function to carry out such anoperation test method.

BACKGROUND ART

In the automobile industory or the machinery industory, there has beenincreased demand for detectors capable of precisely detecting a physicalquantity such as force, acceleration or magnetism. Particularly, it isrequired to realize small detectors capable of detecting physicalquantities having two dimensional or three dimensional components.

To meet such a demand, there has been proposed a force detector in whichgauge resistors are formed on a semiconductor substrate such as silicon,etc. to transform a mechanical distortion produced in the substrate onthe basis of a force applied from the external to an electric signal bymaking use of the piezo resistance effect. When a weight body isattached to the detecting unit of the force detector, an accelerationdetector for detecting, as a force, an acceleration applied to theweight body can be realized. Further, when a magnetic body is attachedto the detecting unit of the force detector, a magnetic detector fordetecting, as a force, a magnetism exerted on the magnetic body can berealized. For example, in U.S. Pat. No. 4,905,523, U.S. Pat. No.4,967,605, U.S. Pat. No. 4,969,366, detectors for force, acceleration ormagnetism according to the invention by the inventor of this applicationare disclosed.

In place of the above described detectors utilizing the piezo resistanceeffect, detectors utilizing changes in distance between electrodes areproposed. For example, in the Japanese Patent Application No. 274299/90specification, there is disclosed a detector of a simple structureincluding two substrates oppositely arranged and electrodes formed onrespective substrates. In this detector, one substrate is allowed to besubjected to displacement on the basis of a physical action such asforce, acceleration, or magnetism, etc. to be detected. An applied forcechanges the distance between electrodes formed on both the substrates.By this displacement the applied force is detected as a change of anelectrostatic capacity between both the electrodes, Alternatively, thereis also disclosed a method in which a piezo electric element is putbetween both electrodes to detect a change of the distance between theelectrodes as a voltage produced from the piezo electric element. If anexternal force is directly exerted to one substrate, this detectorfunctions as a force detector for detecting an external force exerted.Further, if a weight body is connected to one substrate so that thesubstrate is subjected to displacement on the basis of an accelerationexerted on the weight body, this detector functions as an accelerationdetector for detecting an acceleration exerted. In addition, if amagnetic body is connected to one substrate so that the substrate issubjected to displacement on the basis of a magnetism exerted on themagnetic body, this detector functions as a magnetic detector fordetecting a magnetism exerted.

Generally, in the case of providing apparatuses for detecting anyphysical quantity as commercial products, there takes place thenecessity of carrying out an operation test as to whether or not thisdetector outputs a correct detection signal. As such an operation test,there is adopted a method of actually exerting a physical quantity to bedetected on that detector to examine a detection signal at that time.For example, in the case of an acceleration detector, there is employeda method of actually applying, from a predetermined direction, anacceleration of a predetermined magnitude to the detector to judgewhether or not a detection signal at that time is a correct onecorresponding to the applied acceleration. However, in order to carryout such an operation test, a test equipment exclusively used thereforis required, and the test work is complicated or troublesome, requiringmuch time. Especially, the quantity of detectors which can be tested byan exclusive test equipment is limited, resulting in loweredproductivity. Accordingly, such a conventional test method is notsuitable as the method of testing the operation of detectors massproduced.

A first object of this invention is to provide a method capable ofconducting a simple operation test of apparatuses for detecting aphysical quantity utilizing changes in distance between electrodes, anda second object thereof is to provide a detector having a selfdiagnostic function by this simple operation test method.

DISCLOSURE OF INVENTION Operation test method

An operation test method according to this invention is directed to amethod for testing the operation of a detector including a displacementelectrode supported so that it can be subjected to displacement byapplication of an external force, a fixed electrode fixed to a detectorcasing at a position opposite to the displacement electrode, anddetection means for taking out, as an electric signal, a change of adistance between both the electrodes, thus to detect a physical quantitycorresponding to the external force as an electric signal. Thisoperation test can be grasped in a manner classified into four methodsas described below:

(1) The first method of the operation test according to this inventionresides in a method of applying a predetermined voltage across the fixedelectrode and the displacement electrode, allowing the displacementelectrode to be subjected to displacement by a coulomb force produced onthe basis of the applied voltage, and comparing an electric signaldetected by the detection means in this displacement state with theapplied voltage to thereby test the operation of this detector.

(2) The second method of the operation test according to this inventionresides in a method in which there is further provided a test electrodefixed to the detector casing at a position opposite to the displacementelectrode, the method comprising the steps of applying a predeterminedvoltage across the test electrode and the displacement electrode,allowing the displacement electrode to be subjected to displacement by acoulomb force produced on the basis of the applied voltage, andcomparing an electric signal detected by the detection means in thisdisplacement state with the applied voltage to thereby test theoperation of this detector.

(3) The third method of the operation test according to this inventionresides in a method in which there is further provided a test electrodesupported so that it can be subjected to displacement together with thedisplacement electrode, the method comprising the steps of applying apredetermined voltage across the test electrode and the fixed electrode,allowing the displacement electrode to be subjected to displacement by acoulomb force produced on the basis of the applied voltage, andcomparing an electric signal detected by the detection means in thisdisplacement state with the applied voltage to thereby test theoperation of this detector.

(4) The fourth method of the operation test according to this inventionis resides in a method in which there are further provided a first testelectrode supported so that it can be subjected to displacement togetherwith the displacement electrode and a second test electrode fixed to thedetector casing at a position opposite to the first test electrode, themethod comprising the steps of applying a predetermined voltage acrossthe first and second test electrodes, allowing the displacementelectrode to be subjected to displacement by a coulomb force produced onthe basis of the applied voltage, and comparing an electric signaldetected by the detection means in this displacement state with theapplied voltage to thereby test the operation of this detector.

In accordance with this invention, by applying the above describedoperation test method to a physical quantity detector of the type fordetecting changes in the distance between electrodes as changes in theelectrostatic capacitance, three detectors having a self diagnosticfunction which will be described below can be realized.

(1) A first detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism from the external, and aflexible portion having flexibility formed between the fixed portion andthe working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed to the fixed substrate and formed at a positionopposite to the displacement electrode;

a test electrode fixed to the detector casing at a position opposite tothe displacement electrode and electrically insulated from the fixedelectrode;

detection means for outputting, as an electric signal, a change of anelectrostatic capacitance produced between the displacement electrodeand the fixed electrode; and

voltage application means for applying a predetermined voltage acrossthe test electrode end the displacement electrode,

to detect a force exerted on the working portion on the basis of anelectric signal outputted from the detection means, and to compare theelectric signal outputted from the detection means with the appliedvoltage applied by the voltage application means, thus making itpossible to carry out the operation test.

(2) The second detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism, etc. from the external,and a flexible portion having flexibility formed between the fixedportion and the working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed by the fixed substrate and formed at a positionopposite to the displacement electrode;

a test electrode subjected to displacement together with thedisplacement electrode at a position opposite to the fixed electrode,and electrically insulated from the displacement electrode;

detection means for outputting, as an electric signal, a change of anelectrostatic capacitance produced between the displacement electrodeand the fixed electrode; and

voltage application means for applying a predetermined voltage acrossthe test electrode and the fixed electrode,

to detect a force exerted on the working portion on the basis of anelectric signal outputted from the detection means, and to compare theelectric signal outputted from the detection means with the appliedvoltage applied by the voltage application means, thereby making itpossible to carry out the operation test.

(3) The third detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism, etc. from the external,and a flexible portion having flexibility formed between the fixedportion and the working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed by the fixed substrate and formed at a positionopposite to the displacement electrode;

a first test electrode formed so that the flexible substrate is bent onthe basis of displacement of the first test electrode itself;

a second test electrode fixed to the detector casing at a positionopposite to the first test electrode and electrically insulated from thefixed electrode;

detection means for outputting, as an electric signal, a change of anelectrostatic capacitance produced between the displacement electrodeand the fixed electrode; and

voltage application means for applying a predetermined voltage acrossthe first and second test electrodes,

to detect a force exerted on the working portion on the basis of theelectric signal outputted from the detection means, and to compare theelectric signal outputted from the detection means with the appliedvoltage applied by the voltage application means, thereby making itpossible to carry out the operation test.

Application to piezo electric type detector

Further, in accordance with this invention, by applying the abovedescribed operation test method to a physical quantity detector of thetype for detecting changes in distance between electrodes by using apiezo electric element, three detectors having a self diagnosticfunction which will be described below can be realized.

(1) The first detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism, etc. from the external,and a flexible portion having flexibility formed between the fixedportion and the working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed by the fixed substrate;

a piezo electric element arranged in a manner that it is put between theflexible substrate and the fixed substrate, and for transforming apressure applied by both the substrates to an electric signal to outputthat signal to both the electrodes;

a test electrode fixed to the detector casing at a position opposite tothe displacement electrode and electrically insulated from the fixedelectrode; and

voltage application means for applying a predetermined voltage acrossthe test electrode and the displacement electrode,

to detect a force exerted on the working portion on the basis of anelectric signal outputted from the piezo electric element, and tocompare the electric signal outputted from the piezo electric elementwith the applied voltage applied by the voltage application means,thereby making it possible to carry out the operation test.

(2) The second detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism, etc. from the external,and a flexible portion having flexibility formed between the fixedportion and the working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed by the fixed substrate;

a piezo electric element arranged in a manner that it is put between theflexible substrate and the fixed substrate, and for transforming apressure applied by the both substrates to output that signal to theboth electrodes;

a test electrode subjected to displacement together with thedisplacement electrode at a position opposite to the fixed electrode,and electrically insulated from the displacement electrode; and

voltage application means for applying a predetermined voltage acrossthe test electrode and the fixed electrode,

to detect a force exerted on the working portion on the basis ofelectric signal outputted from the piezo electric element, and tocompare the electric signal outputted from the piezo electric elementwith the applied voltage applied by the application means, therebymaking it possible to carry out the operation test.

(3) The third detector comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction such as force, acceleration or magnetism, etc. from the external,and a flexible portion having flexibility formed between the fixedportion and the working portion;

a fixed substrate fixed to the detector casing so as to oppose or facethe flexible substrate;

a displacement electrode formed at a position where a displacement isproduced by bending of the flexible substrate;

a fixed electrode fixed by the fixed substrate;

a piezo electric element arranged in a manner that it is put between theflexible substrate and the fixed substrate, and for transforming apressure applied by the both substrates to an electric signal to outputthat signal to the both electrodes;

a first test electrode formed so that the flexible substrate is bent onthe basis of displacement of the first test electrode itself, andelectrically insulated from the displacement electrode;

a second test electrode fixed to the detector casing at a positionopposite to the first test electrode, and electrically insulated fromthe fixed electrode; and

voltage application means for applying a predetermined voltage acrossthe first and second test electrodes,

to detect a force exerted on the working portion on the basis of theelectric signal outputted from the piezo electric element, and tocompare the electric signal outputted from the piezo electric elementwith the applied voltage applied by the voltage application means,thereby making it possible to carry out the operation test.

Detector for carrying out detection by difference

Further, a further detector according to this invention comprises:

a flexible substrate including a fixed portion fixed to a detectorcasing, a working portion adapted to receive a force based on a physicalaction from the external, and a flexible portion having flexibilityformed between the fixed portion and the working portion;

a first fixed substrate fixed to the detector casing so as to oppose orface a first plane of the flexible substrate;

a second fixed substrate fixed to the detector casing so as to oppose orface a second plane of the flexible substrate;

a first displacement electrode formed on the first plane of the flexiblesubstrate;

a second displacement electrode formed on the second plane of theflexible substrate;

a first fixed electrode fixed by the first fixed substrate and formed ata position opposite to the first displacement electrode;

a second fixed electrode fixed by the second fixed substrate and formedat a position opposite to the second displacement electrode; and

detection means for outputting, as an electric signal, a differencebetween a change of an electrostatic capacitance produced between thefirst displacement electrode and the first fixed electrode and a changeof an electrostatic capacitance produced between the second displacementelectrode and the second fixed electrode,

to detect a force exerted on the working portion on the basis of theelectric signal outputted from the detection means.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a side cross sectional view showing the basic structure of anacceleration detector of the electrostatic capacitance type to which amethod of testing the operation according to this invention is applied.

FIG. 2 is a bottom view of a fixed substrate 10 of the detector shown inFIG. 1. The cross section cut along the X-axis of the fixed substrate 10of FIG. 2 is shown in FIG. 1.

FIG. 3 is a top view of a flexible substrate 20 of the detector shown inFIG. 1. The cross section cut along the X-axis of the flexible substrate20 is shown in FIG. 1.

FIG. 4 is a side cross sectional view showing a bent state of thedetector when a force Fx in an X-axis direction is exerted at theworking point P of the detector shown in FIG. 1.

FIG. 5 is a side cross sectional view showing a bent state of thedetector when a force Fz in a Z-axis direction is exerted on the workingpoint P of the detector shown in FIG. 1.

FIG. 6 is a circuit diagram showing a circuit for operating the detectorshown in FIG. 1 and a circuit for implementing an operation testthereto.

FIG. 7 is a circuit diagram showing an example of an actual circuitconfiguration of the CV converting circuit shown in FIG. 6.

FIG. 8 is a side cross sectional view showing an actual test method withrespect to the detecting operation in a positive Z-axis direction.

FIG. 9 is a side cross sectional view showing an actual test method withrespect to the detecting operation in a negative Z-axis direction.

FIGS. 10a and 10b are side cross sectional views of an accelerationdetector of the electrostatic capacitance type in which the operationtest method according to this invention is carried out to therebyprovide a function to carry out a self diagnosis.

FIG. 11 is a circuit diagram showing a circuit for operating thedetector shown in FIG. 10a and a circuit for implementing an operationtest thereto.

FIG. 12 is a side cross sectional view of another acceleration detectorof the electrostatic capacitance type in which the method of testing theoperation according to this invention is carried out to thereby providea function to carry out a self diagnosis.

FIG. 13 is a side cross sectional view of a force detector of theelectrostatic capacitance type in which the method of testing operationaccording to this invention is carried out to thereby provide a functionto carry out a self diagnosis.

FIG. 14 is a side cross sectional view of an acceleration detector ofthe piezo electric type in which the method of testing operationaccording to this invention is carried out to thereby provide a functionto carry out a self diagnosis.

FIG. 15 is a top view showing the shape of electrodes formed on theupper surface of the piezo electric element 45 in the detector shown inFIG. 14.

FIG. 16 is a side cross sectional view of a force detector of the piezoelectric type in which the method of testing operation according to thisinvention is carried out to thereby provide a function to carry out aself diagnosis.

FIG. 17 is a side cross sectional view of another force detector of thepiezo electric type in which the method of testing the operationaccording to this invention is carried out to thereby provide a functionto carry out a self diagnosis.

FIG. 18 is a side cross sectional view of an acceleration detector ofthe type to take differences in detection of acceleration components inall directions.

FIGS. 19a and 19b are plane views showing an electrode arrangement inthe detector shown in FIG. 18.

FIG. 20 is a circuit diagram of a circuit for carrying out detection ofan acceleration in a Z-axis direction in the detector shown in FIG. 18and for carrying out the operation test thereof.

FIG. 21 is a graph showing the general relationship between the distanced between electrodes of the capacitance element and the capacitancevalue C.

FIG. 22 is a side cross sectional view showing another embodiment of thedetector shown in FIG. 18.

FIG. 23 is a side cross sectional view showing a further embodiment ofthe detector shown in FIG. 18.

FIG. 24 is a side cross sectional view showing an embodiment in whichthe detector shown in FIG. 18 is constituted with metal.

FIG. 25 is a side cross sectional view showing an embodiment in whichthe detector shown in FIG. 24 is applied to a force detector.

BEST MODE FOR CARRYING OUT THE INVENTION §1 Basic structure of thedetector

Prior to the description of an operation test method according to thisinvention, the structure of a detector to which this invention isapplied and the principle thereof will be briefly described. FIG. 1 is aside cross sectional view showing the basic structure of an accelerationdetector to which this invention is applied. This detector comprises, asthe major component, a fixed substrate 10, a flexible substrate 20, aworking body 30, and a detector casing 40. The bottom view of the fixedsubstrate 10 is shown in FIG. 2. The cross section cut along the X-axisof the fixed substrate 10 in FIG. 2 is shown in FIG. 1. The fixedsubstrate 10 is formed as a disk shaped substrate as shown, and is fixedat the peripheral portion thereof to the detector casing 40. On thelower surface thereof, fan shaped fixed electrodes 11 to 14 and a diskshaped fixed electrode 15 are formed. On the other hand, the top view ofthe flexible substrate 20 is shown in FIG. 3. The cross section cutalong the X-axis of the flexible substrate in FIG. 3 is shown in FIG. 1.The flexible substrate 20 is also formed as a disk shaped substrate asshown, and is fixed at the peripheral portion thereof to the detectorcasing 40. On the upper surface thereof, fan shaped displacementelectrodes 21 to 24 and a disk shaped displacement electrode 25 areformed. The working body 30 is columnar as the upper surface thereof isindicated by broken lines in FIG. 3, and is coaxially connected to thelower surface of the flexible substrate 20. The detector casing 40 iscylindrical, and fixes and supports the peripheral portions of the fixedsubstrate 10 and the flexible substrate 20.

The fixed substrate 10 and the flexible substrate 20 are arranged with apredetermined spacing therebetween at positions in parallel to eachother. While both substrates are a disk shaped substrate, the fixedsubstrate 10 is a substrate having high rigidity such that bending isdifficult to occur, whereas the flexible substrate 20 is a substratehaving flexibility such that when a force is applied, bending occurs. Inthe example shown in FIG. 1, the fixed substrate is caused to have highrigidity by allowing the thickness thereof to be thick, and the flexiblesubstrate 20 is caused to have flexibility by allowing the thicknessthereof to be thin. In addition to the above, they may be caused to haverigidity or flexibility by changing material thereof. Alternatively, byforming a groove in the substrate, or forming a through hole therein,such members may be caused to have flexibility. As long as the fixedsubstrate 10, the flexible substrate 20 and the working body 30 canperform their primary functions, they may be constituted of anymaterial. For example, they may be constituted of semiconductor orglass, etc., or may be constituted of metal. It is to be noted that inthe case where the fixed substrate 10 and the flexible substrate 20 areconstituted of metal, it is necessary to adopt a method of forminginsulating layers between the metal and the respective electrodes inorder not to short circuit the electrodes, or similar methods. Inaddition, respective electrode layers may be constituted of any materialas long as it has conductive property.

It is now assumed that the working point P is defined at the center ofgravity of the working body 30 as shown in FIG. 1, and that aXYZ-three-dimensional coordinate system having the working point P asthe origin is defined as shown. Namely, the X-axis is defined in a rightdirection of FIG. 1, the Z-axis is defined in an upper directionthereof, and the Y-axis is defined in a direction perpendicular to theplane surface of paper and extending toward the back side of the planesurface of paper. If the central portion to which the working body 30 isconnected, the peripheral portion fixed by the detector casing 40, andthe portion therebetween of the flexible substrate 20 are respectivelycalled a working portion, a fixed portion, and a flexible portion, whenan acceleration is applied to the working body 30, bending is producedin the flexible portion, so the working portion is caused to deviatefrom the fixed portion. Assuming now that the entirety of this detectoris mounted, e.g., in an automotive vehicle, an acceleration will beapplied to the working body 30 on the basis of running of the automotivevehicle. By this acceleration, an external force is exerted on theworking point P. In the state where no force is exerted on the workingpoint P, as shown in FIG. 1, the fixed electrodes 11 to 15 and thedisplacement electrodes 21 to 25 are maintained in a parallel state witha predetermined spacing therebetween. It is now assumed thatcombinations of the fixed electrodes 11 to 15 and the displacementelectrodes opposite thereto are called capacitance elements C1 to C5,respectively. Now, when a force Fx in the X-axis direction is exerted onthe working point P, this force Fx allows the flexible substrate 20 toproduce a moment force. As a result, as shown in FIG. 4, bending will beproduced in the flexible substrate 20. By this bending, the spacingbetween the displacement electrode 21 and the fixed electrode 11 isincreased, but the spacing between the displacement electrode 23 and thefixed electrode 13 is decreased. When a force exerted on the workingpoint P is assumed to be --Fx in an opposite direction, bending havingthe relationship opposite to the above will be produced. As statedabove, when a force Fx or --Fx is exerted, any change appears in theelectrostatic capacitance of the capacitance elements C1 and C3.Accordingly, by detecting this change, it is possible to detect theforce Fx or --Fx. At this time, although respective spacings betweendisplacement electrodes 22, 24 and 25 and fixed electrodes 12, 14 and 15partially increase or decrease, their spacings may be assumed to beunchanged as a whole. On the other hand, in the case where a force Fy or--Fy in the Y direction is exerted, changes similar to the above areproduced only in connection with the spacing between the displacementelectrode 22 and the fixed electrode 12 and the spacing between thedisplacement electrode 24 and the fixed electrode 14. Further, in thecase where a force Fz in the Z-axis direction is exerted, as shown inFIG. 5, the spacing between the displacement electrode 25 and the fixedelectrode 15 becomes small. In contrast, in the case where a force --Fzin an opposite direction is exerted, this spacing becomes large. At thistime, the spacings between the displacement electrodes 21 to 24 and thefixed electrodes 11 to 14 also become small or large. In this case thespacing between the displacement electrode 25 and the fixed electrode 15most conspicuously varies. In view of this, by detecting the change ofthe electrostatic capacitance of the capacitance element C5, it ispossible to detect the force Fz or --Fz.

When it is assumed that the electrode area, the electrode interval andthe dielectric constant are represented by S, d and ε, respectively, theelectrostatic capacitance C of the capacitance element is generallydetermined by the following equation:

    C=εS/d.

Accordingly, when the electrode interval becomes short, theelectrostatic capacitance C becomes large, while when it becomes broad,the electrostatic capacitance C becomes small. This detector utilizesthe above mentioned principle to measure changes in the electrostaticcapacitance between respective electrodes, thus to detect an externalforce exerted on the working point P, i.e., an acceleration exerted.Namely, an acceleration in an X-axis direction is detected on the basisof changes in the capacitance between capacitance elements C1 and C3, anacceleration in a Y-axis direction is detected on the basis of changesin the capacitance between the capacitance elements C2 and C4, and anacceleration in a Z-axis direction is detected on the basis of changesin the capacitance of the capacitance element C5.

This invention relates to a method of testing the operation of thedetector based on the above mentioned principle. It is to be noted thatwhile the above described detector is of the electrostatic capacitancetype, in the case of a detector of the piezo electric type, a piezoelectric element is inserted between the flexible substrate and thefixed substrate. In this case, in place of detecting changes in theelectrostatic capacitance, a voltage produced from the piezo electricelement is detected.

§2 Method of testing the operation

A method of testing the operation according to this invention will nowbe described. FIG. 6 is a circuit for operating the detector shown inFIG. 1 and a circuit for implementing the operation test thereto. Here,capacitance elements C1 to C5 correspond to capacitance elements formedat the above described acceleration detector. For example, thecapacitance element C1 is comprised of combination of the fixedelectrode 11 and the displacement electrode 21. Further, CV convertingcircuits 51 to 55 connected to respective capacitance elements C1 to C5have a function to convert electrostatic capacitance values C ofrespective capacitance elements to corresponding voltages V.Accordingly, voltage values V1 to V5 outputted from the CV convertingcircuits 51 to 55 take values proportional to electrostatic capacitancevalues of the capacitance elements C1 to C5. A differential amplifier 71outputs a difference between voltage values V1 and V3 to the terminalTx, and a differential amplifier 72 outputs a difference between voltagevalues V2 and V4 to the terminal Ty. Further, a voltage value V5 isoutputted to the terminal Tz. By making reference to the explanation ofthe structure and the operation of the detector described in §1, it canbe understood that a voltage (V1-V3) obtained on the terminal Tx becomesan acceleration detection value in an X-axis direction, a voltage(V2-V4) obtained on the terminal Ty becomes an acceleration detectionvalue in a Y-axis direction, and a voltage V5 obtained on the terminalTz becomes an acceleration detection value in a Z-axis direction.

It is to be noted that an acceleration in an X-axis or a Y-axisdirection is detected by taking a difference between two voltages by thedifferential amplifier as described above. Such a detection based ondifference can advantageously cancel an error (e.g., temperature error)resulting from the external environment. It is to be noted that whiledetection based on difference is not conducted in connection with anacceleration in a Z-axis direction, this will be described in thesucceeding §4.

The CV converting circuits 51 to 55 and the differential amplifiers 71and 72 which have been described are eventually circuits necessary forallowing this detector to carry out the detecting operation. Theoperation test according to this invention can be carried out by furtheradding voltage generating circuits 61 to 65 and test switches S1 to S5to the above mentioned circuit. Any voltage generating circuits 61 to 65may be employed as long as they are circuits capable of generating adesired voltage. For example, there may be employed such a circuit toconvert digital data outputted from a microcomputer to an analog signalat a D/A converter.

Let now consider the case where test switches S1 and S2 are turned ON inthe circuit shown in FIG. 6. At this time, if there is employed acircuit configuration such that charges having polarities opposite toeach other are delivered from the voltage generating circuit 63 to boththe electrodes of the capacitance element C3, one electrode is chargedpositive and the other electrode is charged negative between the fixedelectrode 13 and the displacement electrode 23. For this reason, anattractive force based on coulomb force is exerted therebetween.Further, if there is employed a circuit configuration such that chargeshaving the same polarity are delivered from the voltage generatingcircuit 61 to the both electrodes of the capacitance elanant C1, arepulsive force based on coulomb force is exerted therebetween. Thus, asshown in FIG. 4, the flexible substrate 20 will produce displacement. Itis seen that this is the same state as the state where a force Fx in anX-axis direction is exerted on the working point P. In this state,detected voltages outputted to respective terminals Tx, Ty and Tz areexamined to determine whether or not they are correct detected valuesindicating that the force Fx is exerted. Eventually, the operation testis carried out by applying voltages from the voltage generating circuits61 and 63 to the capacitance elements C1 and C3 to thereby create thesame state as the state where a force Fx in an X-axis direction isexerted on the working point P to examine detected voltages. If acorrect relationship between an applied voltage and a detected voltageis determined in advance, a quantitative operation test can beconducted. In this operation test, there is no necessity of usingvibrator, etc. to actually apply an acceleration to the working body 30.Namely, only by observing an electric signal outputted when an electricsignal is inputted, the operation test is completed. Accordingly, thework becomes simple as compared to the conventional operation test, andis thus suitable for mass production. The test of the detectingoperation of an acceleration in an --X axis direction may be conductedby applying voltages to capacitance elements C1 and C3 by using theswitches S1 and S3. Further, the test of the detecting operation of anacceleration in a Y-axis direction may be conducted by applying voltagesto capacitance elements C2 and C4 by using the switches S2 and S4. Inaddition, the test of the detecting operation of an acceleration in aZ-axis direction may be conducted by applying a voltage to thecapacitance element C5 by using the switch S5.

In the circuit diagram shown in FIG. 6, it is preferable to employ avoltage generating circuit such that the capacitance values of circuits61 to 65 viewed from the external are constant irrespective of voltagesgenerated. Alternatively, a voltage generating circuit having apredetermined correlation between a voltage generated and a capacitanceviewed from the external may be adopted. Since the voltage generatingcircuits 61 to 65 are connected in parallel with capacitance elements C1to C5 when viewed from the circuit arrangement, if the capacitancevalues of the voltage generating circuits 61 to 65 vary at random, acorrect operation test cannot be carried out. Further, it is requiredfor the CV converting circuits 51 to 55 to detect electrostaticcapacitance values of the capacitance elements C1 to C5 withoutundergoing the influence of voltages applied by the voltage generatingcircuits 61 to 65. An example of a CV converting circuit having such afunction is shown in FIG. 7. The CV converting circuit 50 shown here hasa function to convert an electrostatic capacitance C of a capacitanceelement C0 to a voltage V to output it to the terminal Tout. It is herenoted that a voltage is applied from the voltage generating circuit 60to the capacitance element C0. The CV converting circuit 50 is comprisedof an oscillator circuit 56 and a rectifier circuit 57. The oscillatorcircuit 56 generates an a.c. signal of a predetermined frequency toapply it to the capacitance element C0. The rectifier circuit 57 iscomprised resistors R1 and R2, capacitors C6 and C7, and a diode D1, andserves to convert an electrostatic capacitance of the capacitanceelement C0 supplied with the a.c. signal to a voltage V to output it.The CV converting circuit 50 thus constructed can convert anelectrostatic capacitance C of the capacitance element C0 to a voltage Vwithout undergoing the influence of an applied voltage from the voltagegenerating circuit 60. It is to be noted that the circuit of FIG. 7 isillustrated as an example, and various circuits can be therefore appliedfor the CV converting circuit in addition thereto.

The operation test according to this invention will now be described inconnection with a further actual embodiment. FIG. 8 is a side crosssectional view showing an actual test method with respect to theoperation for detecting a force in a positive Z-axis direction. Thisdetector is comprised of a fixed substrate 80 and a flexible substrate90. At the bottom surface of the flexible substrate 90, a doughnutshaped groove G is dug. The thickness of the portion where the groove Gis dug is thinner than those of other portions. Thus, the flexiblesubstrate 90 is caused to have flexibility at this portion. The fixedsubstrate 80 is connected or bonded to the upper surface of the flexiblesubstrate 90 with a predetermined space being kept therebetween in amanner to cover the upper surface off the flexible substrate 90. Aplurality of fixed electrodes 81 and a plurality of displacementelectrodes 91 are formed at positions opposite to each other on thelower surface of the fixed substrate 80 and the upper surface of theflexible substrate 90, respectively. In this embodiment, the fixedsubstrate 80 and the flexible substrate 90 are comprised of a glasssubstrate and a silicon substrate, respectively. The fixed electrodes 81and the displacement electrodes 91 are comprised of aluminum layersformed on the respective substrates. Further, between the flexiblesubstrate 90 and the displacement electrodes 91, an insulating layer 92such as a silicon oxide film or a silicon nitride film is formed. Insuch a detector, in order to make a state which is equivalent to thestate where a force in a positive Z-axis direction is exerted on theworking point P, it is sufficient to exert an attractive force based oncoulomb force between the fixed electrodes 81 and the displacementelectrodes 91. FIG. 8 shows a method of applying a voltage in this case.Namely, when positive charges and negative charges are respectivelygiven to the fixed electrodes 81 and the displacement electrodes 91 bymeans of power supply V, an attractive force is exerted therebetween. Asa result, the operation test in the state where a force in a positiveZ-axis direction is exerted on the working point P can be conducted.

It is to be noted that, in order to make a state which is equivalent tothe state where a force in a negative Z-axis direction is exerted on theworking point P, it is required to change somewhat the structure of thedetector itself. Namely, as shown in FIG. 9, a plurality of auxiliaryelectrodes 82 are formed on the upper surface of the fixed electrode 80.Here, by using the power supply V, positive charges are given to theauxiliary electrodes 82 and the flexible substrate 90 (siliconsubstrate) and negative charges are given to the fixed electrodes 81 andthe displacement electrodes 91. Thus, polarization takes place betweenthe auxiliary electrodes 82 and the fixed electrodes 81, andpolarization takes place between the displacement electrodes 91 and theflexible substrate 90. As a result, respective portions are charged sothat they have polarities as shown. Eventually, a repulsive force basedon coulomb force is exerted between the fixed electrodes 81 and thedisplacement electrodes 91, resulting in the state where a force in anegative Z-axis direction is exerted on the working point P.

In the operation test in the state where an attractive force is exertedbetween both members, this test can be sufficiently conducted only bytwo electrodes which directly exert coulomb force. However, in theoperation test in the state where a repulsive force is exertedtherebetween, it is required to additionally form an auxiliaryelectrode. It is to be noted that since the description of the structurebecomes complicated, the description of this auxiliary electrode will beomitted in the following respective embodiments.

§3 Detector having an operation test function

In the above described embodiment, the electrode pair for generatingcoulomb force and the electrode pair for constituting a capacitanceelement are the same electrode pair. Namely, the electrode pair forgenerating coulomb force is a pair of the fixed electrode (11 to 15, 81)and the displacement electrode (21 to 25, 82), and the electrode pairfor constituting a capacitance element is exactly the same electrodepair. If the same pairs are commonly used in this way, although there isthe advantage that it is unnecessary to form another electrode for theoperation test, there is the drawback that there occurs limit in thedegree of test and the circuit for test becomes complicated.Particularly, in order for such equipment to circulate as goods on themarket, it is convenient that a detection terminal for outputting adetection signal of a physical quantity and a test terminal for applyinga voltage for test are separately provided. In the detector disclosedbelow, test electrodes are formed in advance, and an electrode pair forgenerating coulomb force and an electrode pair for constituting acapacitance element are constructed by separate electrode pairs.

FIG. 10a is a side cross sectional view of an acceleration detectorprovided with a test electrode for carrying out an operation test methodaccording to this invention. The basic structure is the same as theacceleration detector shown in FIG. 1 wherein a fixed substrate 10 and aflexible substrate 20 are oppositely provided, and respective substratesare fixed at their periphery thereof to a detector casing 40. The fixedsubstrate 10 is a substrate having rigidity, but the flexible substrate20 is thin in thickness thus to have flexibility. On the upper surfaceof the flexible substrate 20, five displacement electrodes 21 to 25 asshown in FIG. 3 are formed. On the other hand, on the lower surface ofthe fixed substrate 10, five test electrodes 11t to 15t are formed, andfive fixed electrodes 11 to 15 are further formed through an insulatinglayer 16. The planar arrangement of the five fixed electrodes 11t to 15tand the planar arrangement of the five fixed electrodes 11 to 15 are thesame as the electrode arrangement shown in FIG. 2. In such a structure,the electrode pairs for constituting capacitance elements C1 to C5 is anelectrode pairs of the fixed electrodes 11 to 15 and the displacementelectrodes 21 to 25, but the electrode pairs for generating coulombforce are pairs of the test electrodes 11t to 15t and the displacementelectrodes 21 to 25. In these electrode pairs, displacement electrodesare commonly used.

FIG. 10b is an embodiment in which five test electrodes 21t to 25t areformed on the flexible substrate 20. Between the test electrodes 21t to25t and the displacement electrodes 21 to 25, an insulating layer 26 isformed. In this case, the electrode pairs for generating coulomb forceare pairs of the test electrodes 21t to 25t and the fixed electrodes 11to 15.

FIG. 11 is an example of a circuit diagram in which this invention isapplied to a detector of a structure as shown in FIG. 10a. A voltagegenerating circuit 60 applies a voltage across the test electrode 11tand the displacement electrode 21 by allowing the test switch S to beturned ON to exert coulomb force therebetween. Thus, the flexiblesubstrate 20 produces bending, resulting in the equivalent state wherean external force is exerted. On the other hand, the CV convertingcircuit 50 detects an electrostatic capacitance of the capacitanceelement C1 comprised of the fixed electrode 11 and the displacementelectrode 21 to output it as a voltage V. Since the fixed electrode 11and the test electrode 11t are electrically insulated by the insulatinglayer 16, the CV converting circuit 50 can carry out detection of theelectrostatic capacitance without being affected by any means by anapplied voltage produced by the voltage generating circuit 60. As theexternal connection terminal of this detector, it is sufficient toprovide a common terminal conducting to respective displacementelectrodes 21 to 25, detection terminals conducting to respective fixedelectrodes 11 to 15, test terminals conducting to respective testterminals 11t to 15t. By confirming whether or not a predeterminedoutput is provided on the detection terminal when a predeterminedvoltage is applied to the test terminal, it is possible to easily carryout self diagnosis.

FIG. 12 shows an embodiment in which electrodes on the flexiblesubstrate 20 side are separately provided without being commonly used.Namely, first test electrodes 21t to 25t are formed on the upper surfaceof the flexible substrate 20, and displacement electrodes 21 to 25 areformed through an insulating layer 26 thereon. Further, the fixedsubstrate 10 side is similar to that in the previously describedembodiment, i.e., fixed electrodes 11 to 15 are formed through aninsulating layer 16 on second test electrodes 11t to 15t. In such astructure, the electrode pairs for constituting capacitance elements C1to C5 are pairs of fixed electrodes 11 to 15 and displacement electrodes21 to 25, but the electrode pairs for generating coulomb force are pairsof the first test electrodes 21t to 25t and the second test electrodes11t to 15t. The both electrode pairs completely separated from eachother are used as the electrode pair.

FIG. 13 is a side cross sectional view of a force detector according toa further embodiment. Within a detector casing 100, a fixed substrate110, a flexible substrate 120, a working body 130, and a auxiliarysubstrate 140 are provided. A detection piece 131 extending from theworking body 130 is protruding through a hole portion 101 provided inthe detector casing 100 to the outside. In this embodiment, the abovedescribed respective components are all comprised of metal. Aninsulating layer 116 is formed on the lower surface of the fixedsubstrate 110, and two fixed electrodes 111 and 112 are further formedthereon. Further, an insulating layer 146 is formed on the upper surfaceof the auxiliary substrate 140, and two test electrodes 141 and 142 arefurther formed thereon. At the outside on the left side of the detectorcasing 100, a detection terminal 151, a common terminal 152, and a testterminal 153 are conducted out (although respective single terminals areonly illustrated in the figure, terminals corresponding to the number ofelectrodes are actually prepared). As a matter of course, respectiveterminals 151 to 153 are electrically insulated from the detector casing100. Further, the respective terminals 151 to 153 are connected to therespective electrodes and the flexible substrate 120 by means of bondingwires 161 to 163. In this detector, although no displacement electrodeis provided on the flexible substrate 120, since the flexible substrate120 is comprised of metal as previously described, the flexiblesubstrate itself has a function of the electrode.

In this detector, when a force is applied to the front end of thedetection piece 131, the flexible substrate 120 produces bending. As aresult, the distance between the flexible substrate 120 (functioning asa displacement electrode) and the fixed electrodes 111 and 112 varies.Accordingly, it is possible to detect a force exerted on the basis ofchanges in the electrostatic capacitance between the detection terminal151 and the common terminal 152. However, since two fixed electrodes areonly provided in the detector of this embodiment, it is only possible tocarry out detection of force components in a two dimensional direction(force components in left and right directions and in upper and lowerdirections). In order to detect force components in a three-dimensionaldirection, it is enough to provide four fixed electrodes at the minimum.Now, in order to carry out the operation test of this detector, it issufficient to carry out the previously described detection processing inthe state where a predetermined voltage is applied across the testterminal 153 and the common terminal 152. By action of coulomb forcebased on an applied voltage, it is possible to create the same state asthe state where an external force is exerted on the detection piece 131.It is to be noted that it is sufficient to similarly provide four testelectrodes at the minimum in order to carry out the operation in athree-dimensional direction.

The several embodiments which have been described are all directed todetectors of the electrostatic capacitance type. This invention can beapplied not only to such detectors of the electrostatic capacitancetype, but also to detectors of the piezo electric type. FIG. 14 is aside cross sectional view of an acceleration detector of the piezoelectric type having an operation test function according to thinsinvention. In the same manner as in the detector of the electrostaticcapacitance type shown in FIG. 1, a fixed substrate 10 having rigidityand a flexible substrate 20 having flexibility are supported by adetector casing 40, and a working body 30 is connected on the lowersurface of the flexible substrate 20. On the lower surface of the fixedsubstrate 10 and the upper surface of the flexible substrate 20, eightelectrodes are formed as described later, respectively. Between theseelectrodes, a piezo electric element 45 is placed. As the piezo electricelement 45, for example, PZT ceramics (solid solution of lead titanateand lead zirconate) may be used. It is sufficient to insert suchceramics between both electrodes. In actual terms, it is preferable tomanufacture a detector by using a method of firstly forming electrodeson the both upper and lower surfaces of the piezo electric element 45and secondly inserting them between both substrates. At this time, suchelectrodes should be inserted between the substrates in the state wherea predetermined pressure is applied in upper and lower directions of thefigure by the substrates. When such a bias pressure is applied,detection can be made not only in the case where the interval betweenupper and lower electrodes is contracted, but also in the case wherethat interval is broadened. FIG. 15 is a top view of the piezo electricelement 45. In this figure, the planar arrangement of eight electrodesformed on the upper surface is clearly illustrated. As shown, theelectrode formed on the upper surface of the piezo electric element 45is comprised of four fixed electrodes 18a to lad (there is employed inthe figure indication of hatching by slanting lines implemented forhelping visual grasp of the pattern), and four test electrodes 19a to19d (there is similarly employed indication of hatching by dotimplemented). Also on the lower surface of the piezo electric element45, four displacement electrodes 28a to 28d and four test electrodes 29ato 29d are formed at exactly the same arrangement as the above. Thecross section cut along the cutting plane lines 14--14 of the piezoelectric element 45 of FIG. 15 is shown in FIG. 14. It is to be notedthat the electrode configuration is not limited to a planar single layerstructure as shown in FIG. 15, but may be of a multi layer stuckedstructure as shown in FIGS. 10a, 10b and 12.

In such a detector of the piezo electric type, a change of the distancebetween opposite electrode pair is detected as a voltage produced acrossboth the electrodes in place of detecting it as a change of theelectrostatic capacitance. Namely, when an acceleration is exerted onthe working body 30, so bending is produced in the flexible substrate20, a partial compressive force or expansive force is applied to thepiezo electric element 45. Thus, voltages are produced in the respectiveelectrode pairs. By recognizing the degree of voltages outputted to therespective electrode pairs, it is possible to detect the direction andthe magnitude in a three-dimensional coordinate of an exertedacceleration. In the detector of the piezo electric type, electrodepairs for detection and electrode pairs for test cannot be commonly usedas in the case of the detector of the electrostatic capacitance type.This is because since an approach is employed to directly detect avoltage produced across the both electrodes, a voltage for test cannotbe applied to the same electrode. For this reason, the electrode pairsfor detection and the electrode pairs for test have to be separatelyprovided. If the electrode arrangement shown in FIG. 15 is implemented,it is possible to mix two kinds of electrodes on the same plane, and tocarry out detection in a three-dimensional direction and the operationtest thereof.

The operation test can be carried out as follows. For example, when anapproach is employed to apply voltages across the test electrodes 19aand 29a and across the test electrodes 19c and 29c, thus to allow anattractive force to be exerted between the test electrodes 19a and 29a,and to allow a repulsive force to be exerted between the test electrodes19c and 29c, if this detector normally operates, predetermined voltagesare produced across the fixed electrode 18a and the displacementelectrode 28a and across the fixed electrode 18c and the displacementelectrode 28c. By monitoring these voltages, it is possible to carry outthe operation test. By applying a voltage across the test electrodes 19band 29b and across the test electrodes 19d and 29d, a test relating tothe direction vertical to the previously described test direction can becarried out.

FIG. 16 is a side cross sectional view of a force detector of the piezoelectric type having an operation test function according to thisinvention. A detector casing 200 is fixed to an industrial machine, etc.by using screw holes 201, and a strain generative body 250 is connectedto the lower part thereof. The strain generative body 250 is comprisedof metal, and a doughnut groove G is formed at the lower surfacethereof. The portion 252 where this groove G is formed is thin inthickness thus to have flexibility. The screws passed through holes 251of the strain generative body 250 are screw fixed into the screw holes202 of the detector casing 200. A detection piece 260 extends from thelower surface at the central portion of the strain generative body 250,and an external force exerted on the front end thereof is transmitted asa moment force relating to the working point P. Electrodes are formed onthe upper surface and the lower surface of a piezo electric element 230serving as the center of this detector, and are in the state where it isput or held by the fixed substrate 210 and the displacement electrodeflat plate 220 with a predetermined pressure. On the upper surfacethereof, four fixed electrodes 218a to 218d and four test electrodes219a to 219d are formed at the same arrangement as the pattern shown inFIG. 15. On the other hand, a single displacement electrode flat plate220 is formed on the lower surface. The eight electrodes on the uppersurface are fixed on the detector casing by the fixed substrate 210, andthe displacement electrode flat plate 220 on the lower surface isconnected .to the central portion on the upper surface of the straingenerative body 250 by means of a transmission body 240. By constitutingthe displacement electrode flat plate 220 with a thick metal platehaving rigidity, it is possible to efficiently transmit a force exertedon the working point P to the piezo electric element 230.

In the force detector of the piezo electric type thus constructed, thedisplacement electrode flat plate 220 is used as a common electrode,thus making possible to carry out detect ion of an external forceexerted on the detection piece 260 by voltages produced on the fixedelectrodes 218a to 218d. In addition, by monitoring voltages produced onthe fixed electrodes 218a to 218d while applying predetermined voltagesthe test electrodes 219a to 219d, it is possible to carry out theoperation test.

In the embodiment shown in FIG. 17, the force detector of theelectrostatic capacitance type shown in FIG. 13 is replaced by a forcedetector of the piezo electric type. In this detector, five fixedelectrodes 111 to 115 are formed at the same arrangement as the planararrangement shown in FIG. 2, thus making it possible to carry outdetection of a force in a three-dimensional direction. Further, fourtest electrodes 141 to 144 are arranged (indication that the electrode142 is arranged backward of the working body 130 and the electrode 144is arranged forward of the working body 130 is omitted), thus making itpossible to carry out the operation test in a three-dimensionaldirection. Between the fixed electrodes 111 to 115 and the flexiblesubstrate 120, a piezo electric element 145 is inserted. By voltagesproduced on the fixed electrodes 111 to 115, detection of an externalforce exerted is carried out.

It is to be noted that the embodiments shown in FIGS. 10a, 10b, 12, 13,14, 16 and 17 are an embodiment provided with electrodes necessary atthe minimum for implementing the operation test method according to thisinvention of the fixed electrode, the displacement electrode and thetest electrode. In the case where an attractive force based on coulombforce is exerted between two electrodes, it is sufficient to provide twoelectrodes as shown in FIG. 8. However, in the case where a repulsiveforce is exerted, an auxiliary electrode is further required as shown inFIG. 9. Accordingly, it is preferable from a view point of practical useto further provide an auxiliary electrode in the structures shown in theabove described respective embodiments.

§4 Embodiment constructed to take a difference in a Z-axis direction

As illustrated in the circuit diagram shown in FIG. 6, the basicacceleration detector shown in FIG. 1 takes a difference for detectionof acceleration components in an X-axis and a Y-axis directions, butdoes not take a difference for detection of an acceleration component ina z-axis direction. Since detection based on difference advantageouslycancels an error due to the external environment such as temperature,etc., it is preferable to take a difference for detection of anacceleration in a Z-axis direction as well. An embodiment for realizingthis is shown below.

The embodiment showing the side cross section in FIG. 18 is anacceleration detector for carrying out detection of accelerationcomponents in all X, Y and Z directions by taking differences. On thelower surface of the fixed substrate 310, five fixed electrodes 11 ,to15 are formed in accordance with the layout shown FIG. 19a. In aflexible substrate 320, a doughnut groove G is dug at the lower surfacethereof, a working portion 321 is formed at the central portion thereof,a flexible portion 322 is formed therearound, and a fixed portion 323 isformed therearound. On the upper surface thereof, five displacementelectrodes 21 to 25 are formed in accordance with the layout shown inFIG. 19b. The above mentioned configuration is the same as the basicconfiguration shown in FIG. 1. This detector characterized in that asecond fixed substrate 330 is further provided, and that a displacementelectrode 326 and a fixed electrode 336 are respectively formed on thelower of the working portion 321 and the upper surface of the secondfixed substrate 330 in a manner that they are opposite to each other.

Detection of an acceleration components with respect to the X-axis andthe Y-axis directions by this detector and the operation test thereofare the same as those of the detector of FIG. 1. However, detection ofan acceleration with respect to the Z-axis direction and the operationtest thereof are carried out by the circuit shown in FIG. 20. Here, acapacitance element C5 is comprised of a fixed electrode 15 and adisplacement electrode 25, and a capacitance element C6 is comprised ofa fixed electrode 336 and a displacement electrode 326. When comparedwith the circuit with respect to the Z-axis direction shown in FIG. 6,this circuit differs from the former in that a voltage generatingcircuit 66 and a CV converting circuit 56 with respect to thecapacitance element C6 are added, and that a difference between voltagevalues V5 and V6 is determined by a differential amplifier 73 to outputit as a detected value with respect to the Z-axis direction. Thus,detected values with respect to X,Y and Z-axis directions are determinedon the basis of differences, thus making it possible to cancel influenceof temperature, etc.

Further, such a detection based on difference is advantageous also inthe following points. The relationship between distance d betweenelectrodes and the capacitance value C of the capacitance element isgenerally as in the graph shown in FIG. 21. When the distance iscontracted by .increment.d from the state where the capacitance valueindicates C0 at the distance d0 so that d0-.increment.d results, thecapacitance value is increased by .increment.C1, resulting inC0+.increment.C1. In contrast, when the distance is widened by.increment.d so that d0+.increment.d results, the capacitance value isdecreased by .increment.C2, resulting in C0-.increment.C2. Here,.increment.C1>.increment.C2. Accordingly, when detection of anacceleration component in a Z-axis direction is made on the basis ofonly the capacitance value of a set of capacitance elements C5, even inthe case of acceleration components of the same absolute, the degree ofchanges in the capacitance value in a positive Z-axis direction and thatin a negative Z-axis direction differ from each other. To cope withthis, it is required to provide any correction circuit. However, whendetection based on difference is carried out as shown in FIG. 20, such aproblem does not arise. For example, in the detector shown in FIG. 18,when an acceleration exerted in a positive Z-axis direction (in an upperdirection in the figure), the capacitance value of the capacitanceelement C5 changes from C0 to C0+.increment.C1, and the capacitancevalue of the capacitance element C6 changes from C0 to C0-.increment.C2.Thus, an output from the differential amplifier 73 becomes equal to avalue corresponding to .increment.C1+.increment.C2. On the contrary,when the same acceleration is exerted in a negative Z-axis direction (ina lower direction in the figure), the capacitance value of thecapacitance element C5 changes from C0 to C0-.increment.C2, and thecapacitance value of the capacitance element C6 changes from C0 toC0+.increment.C1. Thus, an output from the differential amplifier 73becomes equal to a value corresponding to-(.increment.C1+.increment.C2). In this way, an output of the sameabsolute is provided with respect acceleration components of the sameabsolute.

The embodiment shown in FIG. 22 is characterized in that a working body345 and a pedestal 340 are further added to the embodiment shown in FIG.18. A displacement electrode 326 is formed on the lower surface of theworking body 345. In addition, the embodiment shown in FIG. 23 ischaracterized in that the position of the electrode of the embodimentshown in FIG. 22 is varied: respective fixed electrodes 11 to 15 areformed on the fixed substrate 330, respective displacement electrodes 21to 25 are formed on the lower surface of working body 345; a fixedelectrode 33 is formed on the lower surface of fixed substrate 310 and adisplacement electrode 326 is formed on the upper surface of flexiblesubstrate 320.

The above described respective embodiments FIGS. 18, 22 and 23 aresuitable for constituting respective substrates with glass orsemiconductor (an insulating layer is formed between the substrate andthe electrode in this case). On the other hand the acceleration detectorshown in FIG. 24 is directed the example suitable for constituting thesubstrate with metal. In this embodiment, members 410, 420, 425, 430 440and 450 are all comprised of metal. On the lower surface of the member410, five fixed electrodes 11 to 15 are formed through an insulatinglayer 418. Further five displacement electrodes 21 to 25 are formedthrough an insulating layer 428 on the upper surface of the member 420,and a doughnut shaped displacement electrode 426 is formed through aninsulating layer 429 on the lower surface of the member 420. A member425 connected on the lower surface of the member 420, and the lower endof the member 425 is connected to a member 450 through a diaphragm 435.Further, a doughnut shaped fixed electrode 436 is formed through aninsulating layer 438 on the upper surface of the member 430. When anacceleration is exerted on the member 450, the diaphragm 435 is bent, sothe member 420 is subjected to displacement through the member 425. Theprinciple of detection of displacement is as described above.

In the embodiment shown in FIG. 25, the acceleration detector shown inFIG. 24 is applied to a force detector wherein the configuration of thelower half is replaced by a metal member 431 (flexible substrate). Themember 420 is subjected to displacement on the basis of an externalforce exerted on the front end of the detection piece 432. Thus,detection of this external force is carried out.

§5 Other embodiments

While this invention has been described in connection with the severalembodiments shown, this invention is not limited to such embodiments,but may be carried out in various forms in addition thereto. Forexample, as the arrangement of respective electrodes, variousarrangements may be taken in addition to the above describedembodiments. Further, the numbers of respective electrodes are notlimited only to those in the above described embodiments. How manynumber of fixed electrodes, displacement electrodes and test electrodesare formed and/or where they are formed are the matter suitablychangeable in design. Further, while, in the above described embodiment,there was disclosed the example where the arrangement of eightelectrodes shown in FIG. 15 is applied to a detector the piezo electrictype, it is a matter of course that this arrangement can be applied to adetector of the electrostatic capacitance type. As compared to anemployment of the structure in which two electrode layers are stacked asin the detector shown in FIG. 10a, 10b or 12, the arrangement of asingle electrode layer as shown in FIG. 15 becomes simple in themanufacturing process. This arrangement is rather preferable in the massproduction.

While, in the above described embodiments, the method of forming a metallayer such as aluminum on a semiconductor substrate to use it as anelectrode is mainly disclosed as an example, such an electrode may beformed by using any method. For example, there may be employed a methodof forming an impurity diffused region in a semiconductor substrate touse it as an electrode. Further, if the fixed substrate or the flexiblesubstrate is formed with metal, this substrate itself may be used as anelectrode. Accordingly, in this invention, it is not necessarilyrequired that the electrode is separate from the substrate. In addition,while, in the above described embodiments, the acceleration detectorsand the force detectors have been described, if the working body isconstituted with a magnetic material, it is possible to carry outdetection of a force based on magnetism. Namely, this invention issimilarly applicable to detectors for magnetism.

Industrial Applicability

A method of testing the operation according to this invention is widelyapplicable to force detectors, acceleration detectors or magneticdetectors for detecting a physical quantity by making use of changes indistance between electrodes. Further, detectors having a function tocarry out this operation test can carry out the operation test by asimple method, and can be therefore utilized with high reliability inpractical use. Accordingly, it can be expected that this invention isapplied to automotive vehicles or industrial robots.

I claim:
 1. A detector for a physical quantity having a self-testingfunction, the detector comprising:a tubular detector casing; acontinuous flexible substrate placed inside the casing, said flexiblesubstrate having an outer peripheral portion supported by an inner wallof the casing; a fixed, rigid substrate placed inside the casing abovesaid flexible substrate and fixed to the casing so as to face saidflexible substrate with a spacing therebetween; a working body connectedto a lower surface of said flexible substrate at a central portionthereof so that said flexible substrate is bent when a force caused byan external physical action is applied to said working body; adisplacement electrode supported on an upper surface of said flexiblesubstrate so as to be displaced when the flexible substrate is bent; afixed electrode supported on a lower surface of said fixed substrate soas to face said displacement electrode; a test electrode supported onsaid lower surface of said fixed substrate so as to face said flexibleelectrode, said test electrode and said fixed electrode beingelectrically insulated from each other; detection means for generatingan electric signal which indicates a change of an electrostaticcapacitance between said displacement electrode and said fixedelectrode; and voltage application means for applying a predeterminedvoltage across said test electrode and said displacement electrode forcalibration purposes.
 2. A detector for physical quantity having aself-testing function, .the detector comprising:a tubular detectorcasing; a continuous flexible substrate placed inside the casing, saidflexible substrate having an outer peripheral portion supported by aninner wall of the casing; a fixed, rigid substrate placed inside thecasing above said flexible substrate and fixed to the casing so as toface said flexible substrate with a spacing therebetween; a working bodyconnected to a lower surface of said flexible substrate at a centralportion thereof so that said flexible substrate is bent when a forcecaused by an external physical action is applied to said working body; adisplacement electrode supported on an upper surface of said flexiblesubstrate so as to be displaced when the flexible substrate is bent; afixed electrode supported on a lower surface of said fixed substrate soas to face said displacement electrode; a test electrode supported onsaid upper surface of said flexible substrate so as to face said fixedelectrode, said test electrode and said displacement electrode beingelectrically insulated from each other; detection means for generatingan electric signal which indicates a change of an electrostaticcapacitance between said displacement electrode and said fixedelectrode; and voltage application means for applying a predeterminedvoltage across said test electrode and said fixed electrode forcalibration purposes.
 3. A detector for physical quantity having aself-testing function, the detector comprising:a tubular detectorcasing; a continuous flexible substrate placed inside the casing, saidflexible substrate having an outer peripheral portion supported by aninner wall of the casing; a fixed, rigid substrate placed inside thecasing above said flexible substrate and fixed to the casing so as toface said flexible substrate with a spacing therebetween; a working bodyconnected to a lower surface of said flexible substrate at a centralportion thereof so that said flexible substrate is bent when a forcecaused by an external physical action is applied to said working body; adisplacement electrode supported on an upper surface of said flexiblesubstrate so as to be displaced when the flexible substrate is bent; afixed electrode supported on a lower surface of said fixed substrate soas to face said displacement electrode; a first test electrode supportedon said upper surface of said flexible substrate so as to face saidfixed substrate, said first test electrode and said displacementelectrode being electrically insulated from each other; a second testelectrode supported on said lower surface of said fixed substrate so asto face said first test electrode, said second test electrode and saidfixed electrode being electrically insulated form each other; adetection means for generating an electric signal which indicates achange of an electrostatic capacitance between said displacementelectrode and said fixed electrode; and voltage application means forapplying a predetermined voltage across said first test electrode andsaid second test electrode for calibration purposes.